Signal transmission cables mainly consist of coaxial cables, twisted pair cables and flexible flat cables. Known examples of cables having superior flexibility and bendability include a flexible flat cable that uses a polyolefin resin for a lowly conductive layer (see Patent Document 1), and a flexible flat cable in which a flexible printed circuit board is wound in the form of a spiral around a core material (see Patent Document 2). However, although both of these cables are resistant to bending, they do not demonstrate elasticity.
In the case of designing a high-speed signal transmission cable, the distance between two conductor wires and the dielectric surrounding the conductor wires are known to affect transmission properties. Consequently, it is a common practice to maintain a constant distance between the two conductor wires by immobilizing with resin and the like, while the idea of separately winding two independent conductor wires to transmit signals while demonstrating elasticity has yet to be conceived.
On the other hand, although coaxial cables are typically rigid and are known to be imparted with elasticity by forming into a so-called curl cord, none of these coaxial cables impart elasticity by winding around an elastic core material.
In addition, twisted pair cables consist of tightly twisting two conductor wires, and none of these cables have been imparted with elasticity.
In addition, an example of an elastic wire is disclosed in Patent Document 3 in the form of a method that uses a covering apparatus to wind two conductor wires by S/Z twisting (two directions) around a core material such as an elastic long fiber followed by bundling a plurality of the wound wires into a single wire. According to this patent document, this elastic wire is disclosed as being able to be used as earphone cords or USB single cables. However, there is no description whatsoever regarding transmission properties.
When a conductor wire is wound in one direction around an elastic core material, a large amount of winding torque remains resulting in the occurrence of twisting. Consequently, in the case of winding two conductor wires around an elastic core material, the wires are typically wound by S/Z twisting (in two directions).
Although Patent Document 6, which relates to a signal transmission filament, describes to the effect that a signal transmission thread is wound around a core material, this consists of winding a single metal wire as exemplified by flat copper wire, and does not consist of winding two or more conductor wires. In addition, there is no description relating to transmission properties, and according to findings of the inventors of the present invention, this cable is unable to realize high-speed signal transmission.
With respect to methods used to connect an elastic support and wire, although a technology for winding a wire around an elastic support is disclosed in Patent Document 7, this document discloses technology for a connecting component, does not disclose technology for use as a cable, and does not contain any description whatsoever regarding elasticity or transmission properties.
Although Patent Document 8, which relates to a rotor blade cable, describes to the effect that a conductor wire is wound around an elastic body, this has high tension but does not have elasticity.
Recently, accompanying remarkable progress made in the areas of robots and wearable electronic devices, there are a growing number of cases requiring instantaneous exchange of images (video images) obtained with a camera with an arithmetic processor (computer) (or in other words, high-speed signal transmission).
However, since signal transmission cables lack elasticity, the length of wires at the locations of bends (such as the joints of a robot) is required to be equal to or longer than the maximum length during operation. Consequently, problems occur such as sagging of the cable during operation, cables becoming pinched in or caught on bending portions causing disconnections therein, and cables becoming disconnected from connectors.
In addition, in the case of wearable electronic devices, since the wiring lacks elasticity, these devices require the use of a large jacket and the like, thereby resulting in problems such as being unable to produce wearable electronic devices that closely fit the contour of the body or causing discomfort when worn.
In order to solve these problems, there is a need for a cable several centimeters to several meters in length that has shape deformation tracking ability and enables high-speed signal transmission.
Patent Document 1: Japanese Unexamined Patent Publication No. 2008-47505
Patent Document 2: Japanese Unexamined Patent Publication No. 2007-149346
Patent Document 3: Japanese Unexamined Patent Publication No. 2002-313145
Patent Document 4: Japanese Unexamined Patent Publication No. 2004-134313
Patent Document 5: Japanese Unexamined Patent Publication No. S60-119013
Patent Document 6: Japanese Patent No. 3585465
Patent Document 7: Japanese Unexamined Patent Publication No. 2005-347247
Patent Document 8: U.S. Patent Application No. 2007/264124